Neoview Control Query Default (CQD) Reference Guide (R2.5)

SEQUENCE_GENERATOR_CACHE_INITIAL
Runtime controlsCategory
Controls the initial setting of the internal sequence generator cache size per request. The
cache size is used to set how many unique values are obtained from the sequence generator
per request. The computation starts with the SEQUENCE_GENERATOR_CACHE_INITIAL,
then multiplies it with the SEQUENCE_GENERATOR_CACHE_INCREMENT and compares
it to the SEQUENCE_GENERATOR_CACHE_MAXIMUM. For example, if the defaults
for the CQDs were used, then SEQUENCE_GENERATOR_CACHE_INITIAL would provide
the initial value of “1”. A cache of “1” would be obtained. When the cache was exhausted,
“1” would be multiplied by the SEQUENCE_GENERATOR_CACHE_INCREMENT of
“10”, supplying a new cache of 10 numbers. This dynamic calculation continues to increment
the numbers from “1” to “10” to “100” to “1000” to “10000”. “10000” is the
SEQUENCE_GENERATOR_CACHE_MAXIMUM default, so no additional multiplication
would occur. The maximum would be used from that point on to determine the cache size.
The compiler calculates the optimal sequence generator cache initial setting for an insert
query that obtains values for an identity column from an internal sequence generator.
Description
Value is greater than or equal to 1.Any unsigned integer
The default value is ‘1’.
Values
The initial value is the starting number of values retrieved from the sequence generator
object. The default is ‘1’ because this would accommodate single insert scenarios. If single
row insertions are allowed on tables with identity columns you don’t want to retrieve more
than one value, otherwise there are unnecessary gaps.
However, if all inserts are rowset inserts performed as part of loads, this initial value could
be set higher depending on the expected minimal number of rows that are inserted. It may
make sense to do this for specific load jobs. For example, session level, or at a service level
used for certain loads. That way, the slow initial ramp-up can be avoided.
Usage
Not applicableProduction usage
You need to be careful about setting a value higher than 1 if single inserts use this setting,
because you end up with unused values every time an insert is done, or gaps in the identity
column values. Having a higher value would have the same effect if the minimal number
of rows inserted can be less than the value set.
Impact
Set this CQD at the system level. However, overriding the defaults may make sense at a
service level to influence certain loads/insert transactions, or even at a session level for
loads.
Level
Works in conjunction with the CQDs SEQUENCE_GENERATOR_CACHE_INCREMENT
and SEQUENCE_GENERATOR_CACHE_MAXIMUM, and cannot be considered in
isolation. The initial value influences the intermediate ramp-up values generated by the
increment multiplier, and how fast the maximum value is reached.
Conflicts/Synergies
Not applicableAddressing the real
problem
Neoview Release 2.4Introduced in release
Not applicableDeprecated in release
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